1. Field of the Invention
This invention relates to integrated circuit, especially to the output voltage regulator of step-down switching power converters.
2. Background
Integrated power converter plays an important role in power ICs, and has been widely used in electronic products. Step-down switching power converters can be divided into two types, voltage-mode control and current-mode control. Voltage mode step-down switching power converter can greatly decrease the design efforts for its simple control loop. The present voltage-mode step-down switching power converter typically consists of logic control circuit, EA (Error Amplifier), PWM (Pulse Width Modulation) comparator, driver circuit and the output stage, as shown in FIG. 1. In this figure, the output voltage Vout and the reference voltage Vref are connected to EA, generating two signals V1 and V2 to the PWM comparator 40. One of the input terminals of 40 is connected with sawtooth signal Saw, so that 40 adjusts the duty cycle according to V2. Based on pulses generated by 40, the logic control circuit 29 drives a pair of power MOSFETs 31 and 32 through driver circuit 30, realizing power conversion from the input voltage Vin to the output voltage Vout. This is a typical analog controlled power converter, consisting of two power MOSFETs 31 and 32, an inductor 33, a capacitor 34 and the load resistor 35. With development of the CMOS technology, integrated circuits are stepping towards nanometer scale. Driven by Moore's Law, it is necessary to integrate the switching power converter into SoC with nanometer scale process. However, analog circuit design is faced with many challenges such as the decrease of the intrinsic gain and the signal swing. In traditional Voltage-Mode converters, EA with sufficient gain is essential to satisfy the regulation. With nanometer scale process, it is difficult to design high gain EA. Thus it is almost impossible to achieve the regulation requirements when the load varies in wide region.